Negative symptoms are a strong predictor of functional impairment in schizophrenia (SZ). Unfortunately, mechanisms underlying negative symptoms are poorly understood and available treatments are minimally effective. The current study evaluated the novel hypothesis that negative symptoms are associated with an implicit cognitive effort monitoring impairment that manifests during tasks requiring sustained allocation of cognitive control. Outpatients with SZ (n = 33) and healthy controls (CN; n = 29) completed an adapted Demand Selection Task (DST) in which subjects made choices between pairs of cognitive tasks that were implicitly and then explicitly made discrepant in effort demands. The SZ group demonstrated a reduced probability of avoiding the high effort cognitive task in the implicit choice condition but were able to become effort avoidant when the demands of the task were made explicit. Implicit cognitive effort monitoring deficits were associated with greater severity of the expressivity dimension of negative symptoms, but not the motivation and pleasure dimension. The association between diminished expressivity and implicit cognitive effort monitoring deficits is interpreted in light of a novel cognitive resource depletion theory, whereby individuals with SZ may become less expressive due to difficulty implicitly monitoring ongoing cognitive effort exertion and dynamically adjusting effort expenditure as task demands fluctuate.